State estimation is an important function of a power system control center of a power utility company. The state estimator determines an optimal estimate of the current state of the power system, based on the available measurements. The state of the system can be described by a magnitude and phase angle of voltages of each bus in the power system.
The measurements are commonly acquired by supervisory control and data acquisition (SCADA) systems through remote terminal units (RTUs) connected to buses of the power system. SCADA systems provide real-time measurements of bus voltages and power flows among the buses, but these measurements might not be acquired simultaneously. The typical SCADA measurements are voltage magnitude of buses, and active and reactive powers of branches connected to the buses. Various state estimation methods based on SCADA measurements are known, including weighted least square estimator, non-quadratic estimator, least absolute value estimator, leverage point estimator, and least median of squares estimator.
With the increasing use of synchronized phasor measurement units (PMU) in power systems, the PMU devices are becoming a common data source for the state estimation. The PMUs provide synchronized measurements from dispersed locations. Furthermore, the measurement frequency and accuracy of PMUs are better than those of SCADA systems. The PMU measurements typically include phasor voltages of buses, and phasor currents of branches connected to the buses.
The accuracy of state estimation can be increased by including the PMU measurements in the estimation procedure. One of the major challenges of state estimation with hybrid SCADA and PMU measurements is determining an accurate solution in a reasonable time. Accordingly, there is a need for determining a state estimation for power system using hybrid measurements, such as SCADA and PMU measurements.